Why lately is so difficult to conect to wendys wifi ?

On most free open WiFi networks, they make you agree to some terms and conditions before you can use the internet. Just try to search something on the internet and it should pop up.

Is this all Wendy's, or one specific Wendy's? Most like the problem is on the Wendy's side. Ask the manager to reboot their routers.

If it eventually connects it is most likely a problem (or perhaps limitation) of Wendy's network. Note that there is a risk using any unsecured network such as Wendy's, as hackers can see everything you do over it. In addition, many providers of so-called "free" networks collect a lot of data about you and use it for marketing and advertising, and many also sell it to data consolidators. I never use any free network for that reason.